DE19654763B4 - Silencer for a two-stroke engine - Google Patents

Abstract

A muffler (20) for a two-stroke internal combustion engine (1), comprising:
an expansion chamber (31, 32) having an exhaust gas inlet (27) for introducing the exhaust gas flow coming from the exhaust passage (10) of the engine (1) into the expansion chamber (31, 32); and
outside air introduction means (25, 26; 70; 72, 73; 75, 76; 90, 91, 96) connected to a space outside the expansion chamber (31, 32) for sucking outside air and introducing outside air into the exhaust gas flow,
characterized,
in that the outside air introduction means is arranged in the immediate vicinity of the exhaust gas inlet (27) into the expansion chamber (31, 32) in such a way that the exhaust gas flow entering the expansion chamber (31, 32) from the exhaust gas inlet (27) transverses the outside air introduction means flows through and is designed so that a negative pressure for sucking the outside air is generated and the exhaust gas stream before flowing through the expansion chamber (31, 32) is mixed outside air.

Description

The The invention relates to a silencer for one small. air-cooled Two-stroke engine, preferred for use in a small hand-held work machine, such as a hedge trimmer or a chainsaw. In particular, the Invention a silencer, in which an oxidation catalyst element is included to allow exhaust gas determinations fulfill.

With increasing environmental awareness are also supposed to be powered by a small air-cooled two-stroke gasoline engine, for use in a hand-held Working machine, such as a hedge trimmer or a chainsaw, delivered Exhaust gases are detoxified by reducing HC, CO and NOx contained in the exhaust gas becomes. For example, it will be required by the Californian exhaust emission standard "CARB 1999" CO, to reduce total HC (THC) and NOx constituents of exhaust gases, and not higher as 130g / bhp-h, 50g / bhp-h and 4g / bhp-h, respectively, from the year 1999th

Around to meet these emission regulations, gave there are different suggestions for example, the shape of an inlet channel, an outlet channel or a flushing channel a combustion chamber or a cylinder of an internal combustion engine improve, and an exhaust gas cleaning agent, such as an oxidation catalyst element to be installed in an exhaust system. However, none of the suggestions showed satisfactory Results.

When activities to adapt to the exhaust gas regulations, the present inventors have already silencer proposed, each outside on a body an internal combustion engine are to attach a flow of exhaust gas from an outlet channel of the internal combustion engine directly into the muffler, and being in the muffler contain in a certain way an oxidation catalyst element is to clean the exhaust. In particular, a silencer was used with proposed therein an oxidation catalyst assembly, prepared by placing an oxidation catalytic element in the form of a catalytic tissue via a radio-barrier wire mesh, and complete or mostly partially covering the peripheral edge of the oxidation catalytic Elements with side walls at the Circumference of the wire grid to form a substantially U or pointed V-shaped oxidation catalyst element (Example 1 of Japanese Patent Application No. 09-112258). One other muffler has an oxidation catalyst element that is a gas-permeable porous metallic Element, which is arranged on an exhaust gas inlet channel of the muffler is (Example 2 of Japanese Patent Application No. 09184418 A).

at this conventional Examples 1 and 2 carries however, the structure of the muffler itself as well as the material, the shape and the arrangement of the oxidation catalyst element and the like. Not necessarily to achieve the desired Emission control performance at. Furthermore, no special measures met to the mounting properties of the muffler to improve the internal combustion engine, as well as the assembly, the Design freedom and the like. Furthermore, the difficulties the temperature rise due to the reaction (combustion oxidation) the exhaust gas under the catalytic action of the oxidation catalyst element not considered.

Of the Applicant of the present invention has further developed the following muffler (Japanese Patent Application No. 09273416 A). The muffler has an expansion chamber into which an exhaust gas stream from an exhaust passage of an internal combustion engine introduced becomes, a partition plate through which, the expansion chamber vertical is divided into first and second expansion chambers, as well as a Oxidation catalyst element made of gas-permeable, porous, metallic material manufactured, which is provided on the partition plate to the exhaust gas from the first expansion chamber through the oxidation catalyst element to lead to the second chamber.

at this silencer confirmed in particular, that the THC content of the exhaust gas compared with the conventional examples 1 and 2 significantly is reduced. However, no satisfactory result was obtained in reducing the CO content.

To reduce the CO content of the exhaust gas, it is necessary to react CO with O ₂ to form CO ₂ (CO + 1 / 2O ₂ → CO ₂ ). However, since the exhaust gas resulting from the combustion of the air-fuel mixture in the cylinder of the internal combustion engine undergoes further oxidation (combustion) in the first and second expansion chambers under the oxidation promoting effect (combustion promoting effect) of the oxidation catalyst element, the exhaust gas is contained in the second expansion chamber not enough O ₂ . As a result, the reaction of CO + 1 / 2O ₂ → CO ₂ can not proceed sufficiently, so that the reduction of the CO content is insufficient.

From DE-GM 7041152 a silencer for a motor vehicle engine having the features of the preamble of claim 1 is known. There is the outside air introduction of the expansion chamber downstream.

From the DE 44 07 088 A1 Another generic silencer is known in which the expansion chamber is arranged upstream of a mixing chamber, in which then outside air is introduced.

The US-5 457 290 shows a silencer built-in catalyst element.

aim the invention is to provide a silencer for a two-stroke engine, which by a relatively simple structure effectively the CO content of the exhaust gas can reduce.

Around To achieve this goal is a generic muffler with the characteristics of characterizing part of claim 1 proposed.

A preferred embodiment the external outside air intake means comprises a Venturi tube with a constriction and an outside air inlet tube, the Venturi tube is arranged such that exhaust gas through this can blow through, wherein the outside air introduction tube is a connection between the bottleneck of the Venturi tube and the outside of the expansion chamber forms. Preferably, the Außenlufteinführrohr with his supreme outside the expansion chamber arranged and with its lower end in the course the exhaust stream from the outlet channel, at the lower end by the exhaust gas flow to a negative pressure generate, wherein the Außenlufteinführrohr by the negative pressure under suction external air into the expansion chamber introduces.

In the muffler of the present invention, outside air under suction is introduced into the expansion chamber through the outside air inlet means using the exhaust gas flow. The introduction of outside air into the expansion chamber increases the amount of O ₂ in the expansion chamber, thereby promoting the oxidation of CO ₂ . As a result, the CO content of the exhaust gas discharged to the outside is remarkably lower.

When Means for feeding of outside air into the expansion chamber can be an external device, such as an air pump. However, such a device is for one small air-cooled Two-stroke gasoline engine in a hand-held working machine with regard to on weight, cost, usability and the like. Not recommended. In contrast, the outdoor air inlet means according to the invention has a simple structure and is economically advantageous.

In a preferred embodiment the silencer according to the invention is an exhaust gas coolant near an exhaust gas outlet channel for discharging the exhaust gas out of the expansion chamber to the outside, wherein the exhaust gas coolant mixes outside air into the exhaust gas through the exhaust gas flow.

In a further preferred embodiment the silencer according to the invention is the expansion chamber through a partition plate vertically into a first Divided expansion chamber and a second expansion chamber. One Oxidation catalyst element may be the outside air inlet means be connected downstream and here is attached to the partition plate in such a way that exhaust from the outlet channel from the first expansion chamber through the exhaust gas cleaner into the second Is passed expansion chamber. The first expansion chamber is with the outside air inlet means Mistake.

In a further preferred embodiment comprises the oxidation catalyst element a gas permeable Foam.

The Invention will now be described with reference to exemplary embodiments to the attached drawings described.

1 is a vertical section through an embodiment of the muffler according to the invention in combination with a two-stroke engine to which the muffler is mounted;

2 is a top view of the in 1 shown silencer;

3 is a section along line III-III in the direction of arrows in 1 ;

4 is a sectional view taken along line IV-IV in the direction of the arrows in 1 ;

5 is a vertical section of another embodiment of the muffler according to the invention in combination with a two-stroke engine to which the muffler is mounted;

6 is a top view of the muffler of 5 ;

7 is a sectional view taken along line VII-VII in the direction of the arrows in 5 ;

8th is a sectional view taken along line VIII-VIII in the direction of the arrows in 5 ;

9 FIG. 10 is an enlarged sectional view of an embodiment of the exhaust gas refrigerant in the muffler. FIG from 1 ;

10 is an enlarged sectional view of another embodiment of the exhaust gas refrigerant in the muffler in 5 ;

11 Graphically shows the results of comparative experiments for the THC content between the in 1 shown silencers and conventional silencers;

12 shows graphically test results for the CO content between the in 1 shown silencers and conventional silencers;

13 shows another embodiment of the outside air intake means in the silencer according to the invention;

14 shows a further embodiment of the outside air inlet means in the muffler according to the invention;

15 shows a still further embodiment of the outside air inlet means in the silencer according to the invention.

in the following will be executions the invention with reference to the attached Drawings described.

1 and 2 show an embodiment of the silencer according to the invention in combination with a two-stroke engine. In the illustrated embodiment, the internal combustion engine 1 a small air-cooled two-stroke gasoline engine with Schnürle-flushing (hereinafter simply referred to as internal combustion engine), which is included as a power source in a hand-held work machine, such as a hedge trimmer or a chainsaw, and whose capacity is for example about 23 cm ³ . The internal combustion engine 1 includes a cylinder 2 with a hemispherical combustion chamber 5 that with a spark plug 15 equipped, a crankcase 3 that attaches to the bottom of the cylinder 2 connects, as well as a piston 4 that in the cylinder 2 is used. The internal combustion engine 1 includes an inlet channel 7 that with an air-fuel mixture feed path 8th a carburetor is connected, and an exhaust passage 10 , with a silencer to be described below 20 is connected (left or right in 1 ), and further includes a pair of scavenging passages (not shown) at the front and rear sides, respectively. These channels are on the internal combustion engine 1 provided as follows.

In a standard internal combustion engine, the vertical reciprocating motion of the piston becomes 4 over a connecting rod 11 in a rotational movement of a crankshaft 12 converted to a balancing weight 14 is attached, and the output of the crankshaft is used as a driving force of the hand-held work machine.

The silencer 20 This version is at the mouth of the outlet 10 of the cylinder 2 of the internal combustion engine 1 over a heat insulating plate 22 appropriate. The silencer 20 has an expansion chamber, here by a vertical direction (parallel to the longitudinal direction of the internal combustion engine 1 ) extending partition plate 40 in a first chamber 31 and a second chamber 32 is divided. As a partition plate 40 serves a stainless steel plate (SUS plate) with a thermal conductivity as low as about one third of that of a conventional carbon steel plate.

The first expansion chamber 31 is bounded by a double-walled section, which is a rectangular tubular inner wall panel 41 with according to 1 right and left openings and a box-like outer wall panel 36 with one according to 1 has right opening, and is through a partition plate 40 limited, whereby one obtains a rectangular parallelepiped-like shape (see also 3 ). The outer wall plate 36 is with a reinforcement plate 24 disguised in one place, that of the mouth of the outlet channel 10 corresponds to and with an exhaust gas inlet passage 27 is provided to a flow of exhaust gas from the outlet channel 10 in the muffler 20 to introduce (s. 1 and 3 ).

The inner wall panel 41 and the outer wall panel 36 are combined with each other in such a way that bending sections 41a the inner wall panel 41 one of which is the internal combustion engine 1 is adjacent and the other is opposite, and opposite portions of the outer wall panel 36 are connected to each other, for example, by welding, and that the remaining portions are held at a suitable distance from each other, which forms an air gap Sa. The outer wall plate 36 includes a plate 36A that the internal combustion engine 1 is adjacent, and a distal plate 36B whose bending edges are connected to each other.

The second expansion chamber 32 is bounded by a double-walled section which is a box-like inner wall panel 42 comprising a left opening, and by a box-like outer wall panel 37 according to 1 has a left opening, and is through the partition plate 40 limited so that it receives a rectangular parallelepiped shape. The inner wall panel 42 and the outer wall panel 37 are combined with each other such that a bending section 42a the inner wall panel 42 , the internal combustion engine 1 is adjacent, and an opposite section of the outside wall plate 37 are connected to each other, for example by welding, and that the remaining portions are held at a suitable distance from each other, which forms an air gap Sb.

The partition plate 40 is at the periphery between edges 36a . 37a the outer wall panels 36 . 37 held, which the outer walls of the first and second expansion chambers 31 . 32 represent, and is by a predetermined number of bolt nuts 45 airtight clamped.

As in 2 shown are the tops of the outer wall panels 36 ( 36B ) 37 along the partition plate 40 with a required number (four each in this case) of side-by-side, elongated or web-shaped openings 38 . 39 Mistake.

In a lower section of the separating plate 40 passes through an oxidation catalyst element 50 as an exhaust gas cleaner, the separating plate 40 So it's in both the first expansion chamber 31 as well as in the second expansion chamber 32 projecting and having a gas-permeable foam having a rectangular parallelepipedic shape. In particular, in a lower portion of the partition plate 40 a rectangular catalyst element mounting hole 40a educated. A bowl 52 stainless steel (SUS) in the form of a rectangular tube is through the catalyst element mounting hole 40a used, and the shell 52 is by an L-shaped fastener 54 made of metal on the separating plate 40 attached. The oxidation catalyst element 50 is on the shell 52 attached. According to 1 are at the left end of the bottom and at the middle of the right end of the top of the cup 52 Clamps or bending tabs 52a . 52b provided, which are bent from the position shown in dashed lines in the position shown by solid lines, to thereby the oxidation catalyst element 50 to keep.

In this way, the oxidation catalyst element 50 through the shell 52 in the partition plate 40 held. As a result, the shape of the oxidation catalyst element is easier and allows easily size changes, position changes, replacement and an increased number of oxidation cata- sator elements. The shell 52 may be provided with a suitable number of small openings or perforations. This results in a change in the catalytic contact area between the exhaust gas and the oxidation catalyst element 50 , As a result, the course of the catalytic reaction can be controlled.

In the partition plate 40 and over the oxidation catalyst element 50 is a pair of cavities 40b . 40b provided, which at substantially the same height with the outlet channel 10 and the exhaust gas introduction passage 27 in the first expansion chamber 31 protrude. In the cavities 40b . 40b sit heads of bolts 56 for mounting the silencer 20 on the cylinder 2 of the internal combustion engine 1 (see also 4 ).

As in the 1 to 4 shown are at the first expansion chamber 31 clamping bushes 55 . 55 firmly attached, which bridge like the reinforcing plate 24 with the cavities 40b . 40b at substantially the same height of the outlet channel 10 and the exhaust gas introduction passage 27 connect. Further bolt insertion bushings 57 . 57 are in the second expansion chamber 32 coaxial with the clamping bushes 55 . 55 firmly attached.

If the muffler 20 outside on the cylinder 2 is mounted, the bolts are 56 . 56 according to 1 from the right side of the muffler 20 through the bolt insertion bushes 57 . 57 in the clamping bushes 55 . 55 inserted and then turned to male threaded leading end portions of the bolts 56 . 56 in internal thread (not shown) in the wall of the cylinder 2 screw in and thereby the silencer 20 over the partition plate 40 and the clamping bushes 55 . 55 close to the cylinder 2 clamp.

If the muffler 20 on the internal combustion engine 1 could be used, one could use bolts with such a length that they are the second expansion chamber 32 and the first expansion chamber 31 traverse so that they according to 1 from the right side of the muffler 20 in the cylinder 2 be screwed. However, with such bolts, the stability and mounting safety could be uncertain because the bolts are extremely long. In contrast, in the present embodiment, the bolts are placed over the separator plate 40 screwed so that the bolts have a shorter length and the strength of the muffler 20 increase. The in the partition plate 40 provided cavities 40b . 40b also contribute to the fact that the bolts 56 . 56 have a further reduced length. As a result, the muffler 20 stable and safe on the combustion engine 1 to be assembled.

Furthermore, the cavities act 40b . 40b as reinforcing ribs of the partition plate 40 to the structural strength of the separation plate 40 and serve to dampen vibrations caused by exhaust pulses and the like.

Near the according to 1 upper right corner of the second expansion chamber 32 is a tailpipe 60 , which forms an exhaust gas outlet channel for discharging exhaust gas to the outside, on a support 59 orthogonal to the pin insertion bushings 57 attached. As in the 2 and 4 shown is that tailpipe 60 arranged such that its one end 60a near the according to 2 Upper right corner and thus at an approximately farthest point of the oxidation catalyst element 50 is arranged, and its other end 60b as the exhaust outlet end a little from the outer wall panel 37 protrudes. The tailpipe 60 is in length, bore diameter and the like. Selected such that it has optimal dimensions in terms of output and noise reduction.

The silencer 20 This embodiment has a relatively large volume compared to those on any engine with approximately the same capacity as that of the internal combustion engine 1 are attached. In particular, the muffler has 20 about 1.5 to 2 times the volume of those mufflers of the above conventional examples 1 and 2 (about 18 times the displacement).

In addition to the above-mentioned structural features, the muffler of this embodiment has an outside air inlet means upstream of the catalyst element 26 immediately adjacent to the exhaust gas introduction passage 27 the first expansion chamber 31 is provided to introduce external air by suction of an introduced exhaust gas flow.

The outside air intake means comprises a venturi 25 with a bottleneck 25a disposed along the exhaust gas flow direction so that exhaust gas can pass therethrough, and an outside air introduction pipe 26 that is a connection between the bottleneck 25a and the air gap 5a manufactures. The venturi 25 and the outside air introduction tube 26 are at the reinforcement plate 24 or the inner wall panel 41 attached, such as by welding or the like. In this embodiment, the venturi has 25 an upstream diameter slightly smaller than the width of the exhaust duct 10 of the internal combustion engine is (substantially equal to the width of the Abgaseinführdurchgangs 27 ). As in 3 shown, the venturi covers 25 not completely the outer end of the outlet channel 10 and the exhaust gas introduction passage 27 , and thus are gaps Ra, Rb between the contours of the Venturi tube 25 and the channels / passages 10 . 27 formed when looking from a downstream position. This facilitates the production of the Venturi tube 25 and also has the following reason. By forming the gaps Ra, Rb, the exhaust gas flow can partially vent the venturi 25 bypass. As a result, the exhaust gas flow is not significantly delayed. This results in a smooth gas exchange in the combustion chamber 5 , which minimizes power loss.

As in the 4 and 9 shown is on the other end 60b of the tailpipe 60 an exhaust gas coolant with a Venturi tube 66 and an outside air introduction tube 67 provided to rule by a straight output exhaust stream outside air into the exhaust gas.

In the muffler 20 this embodiment, the exhaust gas flow from the outlet channel 10 of the internal combustion engine 1 first in the first expansion chamber 31 being introduced, being close to sonic velocity mainly through the Venturi tube 25 and partially passes through the gaps Ra, Rb and then expands and distributes, as in 1 shown with dash-dotted arrows, which reduces the exhaust noise.

The thus in the first expansion chamber 31 introduced exhaust gas is then forced into the oxidation catalyst element 50 introduced, which is the partition plate 40 permeated, from an exposed side of the oxidation catalyst element 50 and then passes through pores in the oxidation catalyst element 50 into the second expansion chamber 32 introduced, due to a pressure difference between the first expansion chamber 31 and the adjacent second expansion chamber 32 , by that through the partition plate 40 is disconnected. When passing through the oxidation catalyst element 50 The exhaust gas reacts intensively with oxygen from the first expansion chamber 31 is brought along, that is, it is by the catalytic action of the oxidation catalyst element 50 subjected to intensive combustion oxidation. The thus purified exhaust gas in the second expansion chamber 32 is over the tailpipe 60 and the venturi 66 at the other end 60b of the tailpipe 60 is attached, discharged to the outside.

When the exhaust gas through the venturi 25 passing through as part of the outside air inlet means becomes around the lower end of the outside air introduction tube 26 that with the bottleneck 25a of the venturi 25 is connected, generated by the exhaust stream, a negative pressure. This will be outside the outer wall panel 36 ambient air through the in the outer wall plate 36 formed openings 38 sucked into the air gap Sa and from there through the Außenlufteinführrohr 26 in the Venturi tube 25 sucked, like in 1 shown with dash-colon arrows. As a result, outside air is introduced into the first expansion chamber together with the exhaust gas 31 directed.

If, as described above, outside air into the first expansion chamber 31 is sucked, the O ₂ amount in the first expansion chamber 31 increased to promote the oxidation of CO. As a result, the CO content of the exhaust gases is greatly reduced.

To this effect as well as the muffler 20 to demonstrate this design were before Prepares a silencer with a structure of muffler 20 , but without outside air introduction means (Venturi tube 25 and outside air inlet tube 26 ), ie with a structure in which no outside air enters the first expansion chamber 31 was sucked (conventional example A), and a muffler having a structure in which the oxidation catalyst element 50 from the muffler 20 was removed (conventional example B). Using these mufflers, comparative experiments were carried out under the same conditions. The results are in the 11 and 12 shown.

11 and 12 show that both the CO and the THC content of the exhaust gas in the muffler 20 of this embodiment were significantly reduced when compared to the conventional examples A and B.

When the exhaust gas from the tailpipe 60 is discharged to the outside, outside air through the Außenlufteinführrohr 67 in the Venturi tube 66 sucked and mixed in the just to be discharged exhaust gas, as well as the outside air intake means according to 9 to thereby effectively reduce the temperature of the exhaust gas.

Further, in the muffler 20 this embodiment, the expansion chamber through the partition plate 40 vertically into the first expansion chamber 31 and the second expansion chamber 32 divided. Accordingly, this embodiment has the advantage that the formation of a projection, such as a lug, in which on the internal combustion engine 1 supporting side can be avoided, or to minimize the number of projections in the side, thereby improving the assembly and assembly, compared with such a muffler whose expansion chamber is divided by a partition plate horizontally or longitudinally in halves. The muffler of this embodiment has further advantages in that the volume of the muffler 20 , the volume ratio between the first expansion chamber 31 and the second expansion chamber 32 and the like. Can be easily changed, in comparison with such a muffler whose expansion chamber is divided by a partition plate horizontally or longitudinally in halves.

Further, as the exhaust gas purifier, the oxidation catalyst element 50 used, which has a gas-permeable metallic foam element with a rectangular parallelepipedic shape. As a result, the clogging and clogging is markedly reduced, resulting in reduced gas flow resistance and power loss.

Further, the sides of the first and second expansion chambers 31 . 32 except that side, which is connected to the internal combustion engine 1 supported, formed from double-walled sections, each of the inner wall panels 41 . 42 and the outer wall panels 36 . 37 comprising, wherein the inner and outer wall panels are kept at a suitable distance from each other, so that air gaps Sa, Sb arise. As a result, the temperature of the outer surface of the muffler becomes 20 lowered.

Because also the tops of the outer wall panels 36 ( 36B ) 37 with a required number of openings 38 . 39 near the partition plate 40 are provided, the thermal expansion of the air in the air gaps Sa, Sb is reduced due to the temperature rise. Further, the elevated temperature air in the air gap Sa becomes the first expansion chamber 31 in the muffler 20 sucked in to promote cooling. The air gaps Sa, Sb can communicate with each other, so that cooling air around the entire peripheral portion of the muffler 20 circulates to thereby the muffler 20 to cool altogether.

Furthermore, there is an end of the tailpipe 60 at substantially the farthest point of the oxidation catalyst element 50 , As a result, the temperature of the exhaust gas is effectively reduced before being discharged to the outside.

in the above has been an embodiment of the present invention described in detail. However, the following are Variants possible.

As the outside air intake means can be used in place of the above-described outside air intake means with the Venturi tube 25 and the outside air introduction tube 26 use an alternative. In particular, a curved Außenlufteinführrohr can be 70 use, its upper end 70a outside the first expansion chamber 31 is arranged and its lower end 70b is arranged in the course of the exhaust gas flow, with its opening facing downstream, as in the 5 to 7 to see. By using negative pressure, which is about the lower end 70 is generated by the exhaust gas flow, outside air is in the first expansion chamber 31 sucked. In the alternative embodiment of the outside air inlet means to obtain substantially the same effect as in the embodiment described above.

Further, as the exhaust gas refrigerant, instead of the above-described exhaust gas refrigerant with the Venturi tube 66 and the outside air introduction tube 67 alternatively about a Venturi tube 65 use that on a fastener 68 at a short distance from the other end 60b of the tailpipe 60 is attached.

Through the gap between the other end 60b of the tailpipe 60 and the venturi 65 Outside air is introduced, as in the 8th and 10 shown.

Furthermore, the exhaust gas cleaner 50 a metallic or ceramic matrix or the like. The exhaust gas cleaner 50 can in various ways, for example by gluing, on the partition plate 40 to be appropriate.

In the two embodiments of the outside air intake means described above, the top end of the venturi is the upper one 25 connected outside air introduction tube 26 or the curved Außenlufteinführrohrs 70 disposed in the air gap Sa between the outer wall plate 36 and the inner wall panel 41 is provided, and it is outside air from the in the outer wall panel 36 provided openings 38 via the air gap Sa into the first expansion chamber 31 sucked. As a result, air in the air gap Sa also becomes the first expansion chamber 31 introduced and replaced by the introduced outside air. As a result, the cooling of the first expansion chamber 31 improved.

The air gaps Sa, Sb are formed separately from each other in the above embodiment. However, the air gaps may communicate with each other to form an array of air gaps or a single air gap. With such an arrangement of air gaps or a single air gap is the upper end of the Außenlufteinführrohrs 26 or the curved Außenlufteinführrohrs 70 arranged in the array of air gaps or in the single air gap, and at appropriate locations in the outer wall panels 36 . 37 There is a suitable number of openings. In this case, outside air is introduced through the arrangement of air gaps or the individual air gap in order to displace the air therein. As a result, both the second expansion chamber 32 as well as the first expansion chamber 31 ie the entire muffler 20 , effectively cooled.

As in the 1 and 5 shown dashed, the Außenlufteinführrohr 26 or the curved Außenlufteinführrohr 70 through the outer wall panel 36 extended upward to directly introduce outside air, without passage through the air gap Sa. This embodiment has the advantage that outside air is introduced, which was not yet exposed to the heat of the muffler and thus has a lower temperature. In this embodiment, however, foreign matter, dust or the like could. Through the Außenlufteinführrohr 26 or the outside air introduction tube 70 in the muffler 20 enter. As a result, precautionary measures must be taken. For example, the opening of the upper end of the Außenlufteinführrohrs 26 or the curved Außenlufteinführrohrs 70 be covered with a filter or its upper end portion may be bent.

The outside air introduction means is not limited to the above-described two embodiments. Other embodiments of the outside air intake means are in the 13 . 14 and 15 shown as examples.

This in 13 shown outside air inlet means comprises an outside air introduction tube 72 and a conical hollow element 73 , The outside air inlet tube 72 is with his superiors 72a outside the outer wall panel 36 or disposed in the air gap Sa, and the lower end 72b is at a location near the apex of the conical hollow element 73 associated with this. By an exhaust gas flow from the outlet channel 10 is in the conical hollow element 73 generates a negative pressure. The negative pressure draws in outside air. In this embodiment, the effect of the outside air introduction is further improved, as compared with the outside air intake means, which consists only of the curved Außenlufteinführrohr 70 exists, as in 5 shown.

This in 14 shown outside air introduction means comprises a Außenlufteinführrohr 76 and a cylindrical element 75 that with an opening 75a is provided. The outside air inlet tube 76 is with his superiors 76a outside the outer wall panel 36 or disposed in the air gap Sa, and the lower end 76b is near the opening 75a arranged. By means of the opening 75a the exhaust stream is narrowed so that the velocity of the exhaust gas flow increases. As a result, around the opening 75a creates a negative pressure around. The negative pressure draws in outside air. Again, you get the same effect as the outside air introduction using the Venturi tube 25 according to 1 ,

This in 15 shown outside air inlet means comprises an outside air introduction passage hole 96 placed in a side wall of the inner wall panel 41 is formed, an impeller 90 on the sidewall and concentric with the outside air inlet channel hole 96 is rotatably mounted, and a guide element 91 for guiding a part of the exhaust gas to the wings 92 of the impeller 90 , The impeller 90 rotates through the exhaust flow and generated by rotary motion of the impeller 90 a vacuum around the center of the impeller 90 , The negative pressure draws in outside air.

Out From the above description it can be seen that with the silencer according to the invention for a Two-stroke engine's CO content of exhaust gases with a relatively simple Effectively reduce structure.

A silencer 20 for a two-stroke ver brennungsmotor 1 includes an expansion chamber 31 . 32 into which an exhaust gas flow from the engine 1 is introduced. Near an exhaust inlet 10 from the engine 1 in the expansion chamber 31 . 32 has the muffler 20 an outside air intake 26 to pass outside air into the expansion chamber through the exhaust gas flow 31 . 32 suck. The introduced outside air reduces carbon monoxide (CO) emissions into the environment.

Claims (8)

Silencer ( 20 ) for a two-stroke internal combustion engine ( 1 ) comprising: an expansion chamber ( 31 . 32 ) with an exhaust gas inlet ( 27 ) for introducing the from the outlet channel ( 10 ) of the motor ( 1 ) exhaust gas flow into the expansion chamber ( 31 . 32 ); and one with a space outside the expansion chamber ( 31 . 32 ) connected outside air introduction means ( 25 . 26 ; 70 ; 72 . 73 ; 75 . 76 ; 90 . 91 . 96 ) for sucking in outside air and introducing the outside air into the exhaust stream, characterized in that the outside air introduction means in the immediate vicinity of the exhaust gas inlet ( 27 ) into the expansion chamber ( 31 . 32 ) is arranged in operative connection with the latter such that the exhaust gas from the exhaust gas inlet ( 27 ) into the expansion chamber ( 31 . 32 ) incoming exhaust gas flow around the outside air introduction means or is formed and is designed so that a negative pressure for the suction of the outside air is generated and the exhaust gas stream before flowing through the expansion chamber ( 31 . 32 ) Outside air is added. Silencer according to claim 1, characterized in that the outside air introduction means ( 25 . 26 ) a Venturi tube ( 25 ) with a bottleneck ( 25a ) as well as an outside air introduction tube ( 26 ), wherein the Venturi tube ( 25 ) is arranged so that exhaust gas is blown therethrough, and wherein the Außenlufteinführrohr ( 26 ) a connection between the bottleneck ( 25a ) of the Venturi tube ( 25 ) and the outside (Sa) of the expansion chamber ( 31 . 32 ). Silencer according to claim 1, characterized in that the carbon black introduction means comprises an outside air introduction tube ( 70 ) whose first end ( 70a ) outside the expansion chamber ( 31 . 32 ) and the second end ( 70b ) is arranged in the course of the exhaust gas flow, at the second end ( 70b ) to generate a negative pressure by the exhaust gas flow. Silencer according to claim 1, 2 or 3, characterized by an exhaust gas coolant ( 65 ; 66 . 67 ) near an exhaust outlet ( 60 ) for discharging the exhaust gas from the expansion chamber ( 31 . 32 ) to the outside, the exhaust gas coolant ( 65 ; 66 . 67 ) is formed and arranged to mix by the output exhaust gas flow outside air into the exhaust gas. Silencer according to one of the preceding claims, further characterized by a separating plate ( 40 ), which the expansion chamber ( 31 . 32 ) into a first expansion compartment chamber ( 31 ) and a second expansion sub-chamber ( 32 ), and by an exhaust gas cleaner ( 50 ), in one pass ( 40a ) through the separating plate ( 40 ) is mounted to exhaust from the outlet ( 10 ) via the first expansion compartment chamber ( 31 ) through the exhaust gas cleaner ( 50 ) into the second expansion sub-chamber ( 32 ) introduce. Silencer according to claim 5, characterized in that the exhaust gas cleaner ( 50 ) an oxidation catalyst element ( 50 ). Silencer according to claim 5 or 6, characterized in that the exhaust gas cleaner ( 50 ) comprises a gas-permeable foam. Silencer according to claim 5, 6 or 7, characterized in that at least one of the expansion part chambers ( 31 . 32 ) a double wall structure with an inner wall plate ( 41 . 42 ) and an outer wall plate ( 37 . 38 ), wherein the outer wall plate ( 37 . 38 ) at a distance from the inner wall plate ( 41 . 42 ) is arranged.